One of the issues that recur in air transportation is how to transport a large number of different payloads in the minimum amount of time and at the lowest cost. These payloads may include capital equipment such as heavy mechanical devices and components, pallets of supplies, vehicles, and the like as well as personnel, in some cases. When a fleet of vehicles is used to carry the payloads, each vehicle carries payloads on multiple trips in order for the fleet to transport all of the payloads. The time to transport all these payloads is affected by the number of vehicles in the fleet and the time it takes for each trip. To reduce the cost of transportation, there are a few fundamental approaches. These include reducing the cost of fuel burned, reducing the cost of the vehicles, and increasing the utilization of each vehicle to reduce the number of vehicles required.
Increasing utilization is accomplished by reducing the total time to complete a trip. This includes reducing total time which includes time to travel from point of origin to destination, time maintaining the vehicle, and time for loading and unloading the payload. Reducing the time spent loading and unloading the payload is addressed by using detachable cargo pods that can be loaded and ready before the aircraft is scheduled to fly. When the aircraft is ready, the cargo pods are attached to the aircraft.
Since attaching and detaching the cargo pod takes less time than loading and unloading the cargo, the aircraft spends less time loading and unloading the payload and therefore achieves higher utilization. Higher utilization and reduced cargo handling cost reduces the cost of transportation.
While increased utilization and reduced vehicle cost are significant benefits of using cargo pods, there are also some drawbacks. For example, referring to FIG. 1, the aircraft 10, with four engines 25 in this case, has three cargo pods 20 attached to the relatively flat undersurface 12 of the aircraft 10. The pods 20 are laterally separated and the aircraft landing gear 14 is housed and deployed in the lateral gaps 16 between pods 20. The pods 20 are tall in order to allow carrying of standard containers and large cargo, like vehicles for example. Because the landing gear 14 must extend beyond the full height of the pods 20, the landing gear 14 are also tall, having a length L, measured from a point of attachment to the aircraft to the ground, as shown.
In general, as the length L of the landing gear 14 increases, it becomes heavier. This is because forces generated during ordinary use of the aircraft, such as braking and turning, generate loads transverse to the landing gear strut 15 which result in bending moments on the strut 15. These bending moments are proportional to the force times the length of the strut. Accordingly, longer landing gear experience larger bending moments. To cope with these larger bending moments, more structural cross sectional area is required in the landing gear strut 15. This adds weight. In addition to bending, the strut 15 must be sized to avoid buckling. As strut length increases, larger structural cross sections, which are heavier, are required to avoid the risk of buckling. With heavier landing gear structure, larger actuators will also be required. All these factors adverse impact weight, cost, and required power.
Aerodynamic drag from the pods poses an issue with regard to fuel consumption and aircraft range. Typically, the pods are separated laterally as in FIG. 1 in order to house and deploy landing gear in the gaps between the pods. The landing gear must be deployed between pods in order to keep a reasonable landing gear track, which is the lateral distance between the outer edges of the main landing gear. If the spacing is too wide, the aircraft will not be compatible with runway and taxiway widths. While part of the upper surface of each pod is covered because of the attachment to the aircraft, the other pod surfaces are exposed. But for the issue with landing gear track, the pods could be designed to fit snugly against each other to cover the surface area on the side of the pods. When the aircraft is flying, air passing over the exposed surfaces generates skin friction and creates aerodynamic drag, in the direction opposite the motion of the aircraft. To maintain steady state flight, the drag force must be countered by force (“thrust”) acting in the direction of the motion of the aircraft. Because an engine is used to generate thrust, and the engine burns fuel to generate thrust, more fuel must be burned to sustain greater thrust. So, it is desirable to reduce drag to reduce thrust and the cost of fuel burned. Skin friction drag increases with increasing surface area exposed to the surrounding air flow. Thus, the larger the exposed area the greater the drag. In addition, the pods force the air to accelerate around them. In the passage ways between the pods and between the pods and the aircraft body, there is narrowing in the cross sectional area (air passage ways) available for air to flow through. The air is therefore forced to accelerate and flow faster to get through the narrowed passage ways. The increased air speed increases skin friction drag. It also increases the risk that shocks might form at high subsonic speed. Shocks create drag by dissipating energy in the air, which results in reduced downstream pressures that essentially create suction on the back end of the aircraft that must be overcome with thrust. The acceleration of airflow around the pods also results in increased drag.
Accordingly, there is a need to reduce the amount of surface area on the pods exposed during flight, and to eliminate or reduce narrow air flow passage ways, consistent with maintaining payload volume. Further, there is a need to shorten the landing gear and reduce its weight. Furthermore, other desirable features and characteristics of the configurable air transport with scalloped underbody, described herein below, will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.